Low pressure steam turbine units include an outer casing having a frame with frame members, and an inner casing positioned on the frame members and about a rotor. It is imperative for proper operation of the steam turbine that the inner casing be aligned concentrically with the rotor axis. This is initially accomplished during site installation of the steam turbine engine by jacking or pulling a finished inner casing into a proper position within the frame of the outer casing. Personnel then hand fit liners (shims) between the inner casing and the frame members for the final required clearance before bolting the finish-machined inner casing into place. This requires that contact surfaces on the inner casing, contact surfaces on the frame members, and contact surfaces on the liners there-between be machined to very close tolerances. This has been acceptable and site schedule and manpower needs were considered in the installation of the new unit. However, even under these ideal conditions, new manufacturing tolerances provided a less-than-ideal situation for achieving the intended fit up of the inner casing with the frame of the outer casing.
The less-than-ideal nature of the current situation can be understood when one considers the multiple facets of just one exemplary conventional positioning arrangement. In the exemplary conventional positioning arrangement several appendages may protrude from the inner casing. Each appendage may have, for example, two prongs, and these two prongs may surround a respective frame member of the outer casing. A liner may be placed between each prong and the respective frame member. This results in a plurality of positioning locations, where each locating includes an appendage surrounding two liners which sandwich a respective frame member. After each prong and each frame member is machined the liners are machined to complete the positioning. This machining step is complex, however, because the contact surface on a prong may or may not be parallel to a respective contact surface on an associated liner. Likewise, the contact surface on the frame member may not be parallel to the contact surface on the prong or a respective contact surface on the liner. As a result, not only is a thickness of the liner to be determined and machined, but an orientation of each of the contact surfaces necessary to achieve the proper positioning is to be determine and machined. Any inaccuracy in the determination or machining of one liner will show up as a change in dimension and/or orientation of another liner, producing a cumulative effect and an even greater need for accuracy.
Once on site, any changes that require repositioning of the inner casing become more complex. For example, in the instance where an upgraded turbine unit is to be installed, some or all of the positioning locations may need to be changed due to a design of the upgraded unit resulting in a relocation of the appendages. In this instance much of the original work done during the original installation in the field can no longer be used. As a result, the new positioning locations must be again fit-up in the field. Even as done during initial installation, this work in the field again presents safety concerns because the machining must be done in place, and the place may require scaffolding and/or awkward positioning to be reached by the field personnel.
In order to simplify this difficult field fit-up process, one solution employs a plurality of bolt-type arrangements. Each bolt-type arrangement is threaded through a threaded hole in a prong and rests on the respective contact surface of the associated frame member. In this manner two prongs sandwich the associated frame member, with or without liners/shims in between. Each bolt-type arrangement has an adjustable foot with a contact surface. The bolt-type arrangement is configured to allow the contact surface of the adjustable foot to adjust as necessary to match an orientation of the respective contact surface on the associated frame member. In this manner the adjustable foot accounts for any misalignment between the prong and the frame member. Where used, this arrangement obviates the need for field personnel to determine dimensions and any misalignments between the prong and the associated frame member required for proper positioning of the inner casing. Since several or all of the positioning locations can have these bolt-type arrangements, the difficulty previously associated with positioning the inner casing is significantly reduced.
Limitations associated with the bolt-type arrangement reduce the number of inner casings where the bolt-type arrangement can be used in all positioning locations. Positioning locations which cannot accommodate the bolt-type arrangement must still be fit using the tedious field machining and manual fit-up procedures. Consequently, there remains room in the art for improvement.